Nace CP 1, Course Manual

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RP0285-2002
NACE International 1
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Section 1: General
1.1 Introduction
1.1.1 This standard is intended to serve as a guide for
establishing minimum requirements for the control of
external corrosion on UST systems that are buried,
partially buried, or in contact with the soil.
1.1.2 This standard does not designate specific
practices for every situation because the complexity of
some environmental conditions in which systems are
buried precludes standardization of corrosion control
practices.
1.1.3 This standard does not include corrosion control
methods
based on chemical control of the
environment, internal linings, or the use of tank
construction materials other than mild steel.
1.1.4 This standard does not override applicable
safety codes and should not be used to infringe on the
primary requirement of protecting personnel, the
environment, and equipment.
In any situation, the
corrosion protection design for underground structures
should incorporate all requirements of any applicable
codes, standards, and regulations as determined by
authorities having jurisdiction.
1.1.5 The provisions of this standard shall be applied
under
the responsible direction of competent
individuals. Such individuals must either be registered
professional engineers, NACE International Certified
Corrosion Specialists or CP Specialists, or individuals
qualified
by professional education and related
practical experience. All of the above individuals must
be
able to demonstrate suitable experience in
corrosion control of UST systems.
1.1.6 Deviation from this standard may be warranted
in specific situations provided the objectives expressed
in this standard have been achieved.
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Section 2: Definitions
Anode: The electrode of an electrochemical cell at which
oxidation occurs. Electrons flow away from the anode in
the external circuit. Corrosion usually occurs and metal
ions enter the solution at the anode.
Cathode: The electrode of an electrochemical cell at
which reduction is the principal reaction. Electrons flow
toward the cathode in the external circuit.
Cathodic Disbondment: The destruction of adhesion
between a coating and the coated surface caused by
products of a cathodic reaction.
Cathodic Polarization: The change of the electrode
potential in the active (negative) direction caused by
current across the electrode/electrolyte interface. (See
Polarization.)
Cathodic Protection (CP): A technique to reduce the
corrosion of a metal surface by making that surface the
cathode of an electrochemical cell.
Continuity Bond: A connection, usually metallic, that
provides electrical continuity between structures that can
conduct electricity.
Corrosion: The deterioration of a material, usually a
metal, that results from a reaction with its environment.
Corrosion Potential (E
corr
): The potential of a corroding
surface in an electrolyte relative to a reference electrode
under
open-circuit conditions (also known as rest
potential, open-circuit potential, or freely corroding
potential).
Current Density: The current to or from a unit area of an
electrode surface.
Dielectric Coating: A coating that does not conduct
electricity.
Electrical Isolation: The condition of being electrically
separated from other metallic structures or the
environment.
Electrochemical Cell: A system consisting of an anode
and a cathode immersed in an electrolyte so as to create
an electrical circuit. The anode and cathode may be
different metals or dissimilar areas on the same metal
surface.
Electrode Potential: The potential of an electrode in an
electrolyte as measured against a reference electrode.
(The electrode potential does not include any resistance
losses in potential in either the solution or the external
circuit. It represents the reversible work to move a unit of
charge from the electrode surface through the electrolyte
to the reference electrode.)